Method for the formation of diffusion barrier

ABSTRACT

Electronic components such as semiconductor wafer VLSI and ULSI integrated circuit devices are provided having a robust barrier layer in the device interconnects. The robust barrier layer provides excellent step coverage, low resistance and enhanced adhesion to CVD copper and the interconnect has a double structure of a layer of a barrier material and a metal layer thereon. The metal layer is preferably tungsten and is formed by replacing silicon or other such atoms on the surface of the barrier layer with tungsten metal. A layer of silicon can be formed on the barrier layer, silicon atoms can be formed on the surface by reacting the barrier layer with a silicon containing reactant or a silicon containing barrier layer can be used.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to the making of electronic componentssuch as semiconductor wafer VLSI and ULSI integrated circuit devices,and, more particularly, to a method for forming a robust barrier layerin the device interconnects with excellent step coverage, uniformity,low resistance and enhanced adhesion to CVD-copper and to the electroniccomponents made by the method.

[0003] 2. Description of Related Art

[0004] The demand for manufacturing semiconductor integrated circuit(IC) devices such as computer chips with high circuit speed, highpacking density and low power dissipation requires the downward scalingof feature sizes in ultralarge-scale integration (ULSI) andvery-large-scale integration (VLSI) structures. The trend to smallerchip sizes and increased circuit density requires the miniaturization ofinterconnect features which severely penalizes the overall performanceof the structure because of increasing interconnect resistance andreliability concerns such as fabrication of the interconnects andelectromigration.

[0005] In general, such structures use silicon wafers with silicondioxide (SiO₂) being the dielectric material and openings are formed inthe SiO₂ dielectric layer in the shape of vias and trenches which arethen metallized forming the interconnects. Increased miniaturization isreducing the openings to submicron sizes (e.g., 0.2 micron and lower)and increasing the aspect ratio (ratio of the height of the opening tothe width of the opening) of the features.

[0006] With the decrease of the design rule, copper gets more focus as aconducting material for the interconnect in ULSI and VLSI devices sinceit has lower resistivity and higher electromigration resistance thanaluminum. Copper easily diffuses through silicon dioxide and silicon,however, and a robust barrier layer to prevent copper diffusion isrequired to encapsulate the copper interconnect.

[0007] Step coverage of the diffusion barrier is also critical for theinterconnect. Normally, physical vapor deposition (PVD) does not produceenough material on the side wall of the contact hole or the via, and, asthe minimum feature size decreases, this phenomenon gets more critical.On the other hand, chemical vapor deposition (CVD) offers much betterstep coverage on the side wall of the contact hole and so is thepreferable method for the formation of the diffusion barriers.Furthermore, the diffusion barrier itself must be thin and uniformotherwise, the line resistance may be greater than the resistance ofaluminum interconnects.

[0008] The prior art method for the formation of a diffusion barrier isto deposit a material such as TiN, TiNSi, or Ta, or TaN, or TaSiN by CVDor PVD. CVD copper on these barrier materials has poor adhesion,however, and the copper peels out during a process such as chemicalmechanical planarization (CMP) or in the following integration process.PVD Ta and/or PVD TaN, which is the most common barrier in the priorart, is normally followed by PVD copper as a seed for theelectro-plating of bulk copper to fill the feature. However, due to poorstep coverage on the side wall of the contact or of the trench, it isnot easy to fill the three-dimensional structure completely. Thisphenomenon becomes more serious with the shrinkage of the minimumfeature size of the semiconductor device.

[0009] Broadly stated, the typical multilayer IC electronic component isbuilt up from a number of layers of a dielectric material layer such assilicon dioxide, fluorinated silicon oxide, polymers including polyimideand fluorinated polyimide, ceramics, carbon and other dielectricmaterials. In the processing sequence known in the art as the “DamasceneProcess”, the dielectric layer is patterned using known techniques suchas the use of a photoresist material which is exposed to define thewiring pattern. After developing, the photoresist acts as a mask throughwhich a pattern of the dielectric material is removed by a subtractiveetch process such as plasma etching or reactive ion etching. Using theDamascene Process, openings defining wiring patterns are provided in thedielectric layer, extending from one surface of the dielectric layer tothe other surface of the dielectric layer. These wiring patterns arethen filled with a metal using a filling technique such aselectroplating, electroless plating, chemical vapor deposition, physicalvapor deposition or a combination of methods. This process typicallyincludes planarization of the interconnect metal by removing excessmetal with a method such as chemical mechanical polishing orplanarization. In the Single Damascene Process, vias or openings areprovided in the same dielectric layer and filled with metallization toprovide electrical contact between layers of wiring levels. In the DualDamascene Process, the via openings and the wiring pattern openings areboth provided in the dielectric layer before filling with metallization.This process simplifies the procedure and eliminates some internalinterfaces. These procedures are continued for each layer in theelectronic component until the electronic component is completed.

[0010] In FIG. 5, a dual Damascene line of the prior art is shownconnecting two conductor containing dielectric layers. Dielectric layers31 and 38 contain metallization 32 in layer 31 and metallization 39 inlayer 38. A stud 36 and trench 40 are shown encased by a wall 34 of adiffusion barrier liner. It is this type structure which has been shownto contribute to an interconnected electronic component having a lowelectromigration life.

[0011] The dielectric material provides electrical insulation andelectrical isolation between the copper wiring elements. The openings inthe dielectric layer typically called vias, when filled with aconductive material, are typically referred to as studs. The studs and atrench for a dual Damascene structure provide the verticalinterconnections between the horizontal copper metallization on thevarious layers of the electronic component.

[0012] To avoid metal diffusion between the metal and the dielectric,barrier layers, also referred to as liners, are included in thestructure to contain the copper or other metal and to provide improvedadhesion of the copper lines and studs to the dielectric or othermetallization.

[0013] Bearing in mind the problems and deficiencies of the prior art,it is therefore an object of the present invention to provide amultilayer electronic component including components made by using asingle Damascene process or a dual Damascene process comprising at leastone layer having through openings which are filled with a conductivematerial to form a trench and/or stud which trench and/or studelectrically connects metallization on other layers and which trenchand/or stud has excellent step coverage, uniformity, low resistance andadhesion to CVD-copper.

[0014] It is another object of the present invention to provide a methodfor making a multilayer electronic component having trench and/or studinterconnections including components made using a single Damasceneprocess or a dual Damascene process wherein the trench and/or stud haveexcellent step coverage, uniformity, low resistance and adhesion toCVD-copper.

[0015] A further object of the invention is to provide an interconnectstructure in an electronic component for connecting metallization on onelayer to metallization on another layer with the interconnect havingexcellent step coverage, uniformity, low resistance and adhesion toCVD-copper.

[0016] Still other objects and advantages of the invention will in partbe obvious and will in part be apparent from the specification.

SUMMARY OF THE INVENTION

[0017] The above and other objects, which will be apparent to oneskilled in the art, are achieved in the present invention which relatesin one aspect to an interconnect structure in a multilayer electroniccomponent for connecting metallization layers, the interconnectstructure having excellent step coverage, uniformity, low resistance andadhesion to CVD-copper comprising:

[0018] a dielectric layer having a through opening to a conductor inanother layer;

[0019] a diffusion barrier layer in the through opening in thedielectric layer;

[0020] a metallic layer on the diffusion barrier layer; and

[0021] copper or other metal filling the opening to form theinterconnect structure.

[0022] In a further aspect of the invention a multilayer electroniccomponent is provided such as a VLSI and ULSI integrated circuit devicecomprising:

[0023] a plurality of dielectric layers having metallization therein;

[0024] openings in the form of a trench and/or via extending through atleast one layer and connecting metallization in another layer;

[0025] a diffusion barrier layer in the opening on the dielectric layer;

[0026] a metallic layer on the diffusion barrier layer; and

[0027] copper or other metal filling the opening to electrically connectthe metallization in the dielectric layers.

[0028] In a further aspect of the invention a method is provided formaking multilayer electronic components such as VLSI and ULSI integratedcircuit devices wherein interconnects in the devices have excellent stepcoverage, uniformity, low resistance and adhesion to CVD-coppercomprising the steps of:

[0029] forming a multilayer electronic component layer by layer withdielectric layers having openings therein with metallization formed inthe openings to provide electrical connections between the layers;

[0030] forming a diffusion barrier in the opening on the dielectriclayer;

[0031] forming a metallic layer on the diffusion barrier layer byreacting the barrier layer with a metal containing reactant; and

[0032] filling the opening with copper or other metal to provide aconductor which contacts the metallization in the dielectric layer toanother layer.

[0033] In another aspect of the invention the method comprises the stepsof:

[0034] surface treating the diffusion barrier layer with SiH₄ or othergases containing Si to form a Si rich surface, or forming a thin Sideposit on the diffusion barrier layer, preferably an amorphous Sideposit;

[0035] exposing the treated surface to a conductive metal containingreactant to replace at least part of the Si with the conductive metal;and

[0036] forming the metallic conductor in the opening.

[0037] In a further aspect of the invention the method comprises thesteps of:

[0038] forming the diffusion barrier with a material containing silicon,such as titanium silicon nitride;

[0039] exposing the diffusion barrier layer to a conductive metalcontaining reactant to replace at least some of the silicon with theconductive metal; and

[0040] forming the metallic conductor in the opening.

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The features of the invention believed to be novel and theelements characteristic of the invention are set forth withparticularity in the appended claims. The figures are for illustrationpurposes only and are not drawn to scale. the invention itself, however,both as to organization and method of operation, may best be understoodby reference to the detailed description which follows taken inconjunction with the accompanying drawings in which:

[0042] FIGS. 1A-1C show a sequence of steps for forming a metal richsurface on a dielectric according to a method of the invention.

[0043] FIGS. 2A-2B show a sequence of steps for forming a metal richsurface on the surface of a dielectric according to another method ofthe invention.

[0044] FIGS. 3A-3G show a sequence of steps for forming a dual Damasceneline and interconnection stud structure according to a method of theinvention.

[0045]FIG. 4 shows an elevational view of an interconnect stud structureof the invention.

[0046]FIG. 5 shows an elevational view of an interconnect dual Damasceneline and interconnection stud structure of the prior art.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

[0047] In describing the preferred embodiment of the present invention,reference will be made herein to FIGS. 1A-5 of the drawings in whichlike numerals refer to like features of the invention. Features of theinvention are not necessarily shown to scale in the drawings.

[0048] Referring to FIG. 1A, part of a multilayer electronic componentis shown schematically and comprises a dielectric layer 10 having adiffusion barrier layer 11 thereon. As will be shown more fullyhereinbelow, the dielectric layer 10 is used to form a multilayerelectronic component and typically has openings therein in the form ofvias and/or lines which are coated with a barrier layer 11. FIG. 1Ashows schematically the dielectric layer 10 and the diffusion barrierlayer 11 for convenience.

[0049] The dielectric layer 10 may be made of any suitable dielectricmaterial depending on the application for the electronic component andincludes materials such as silicon dioxide, fluorinated silicon oxide, apolymer such as polyimide, a diamond-like carbon or a spin on glass. Thebarrier layer 11 may likewise be any suitable material that provides adiffusion barrier between the conductor formed in the dielectric and thedielectric. Preferred diffusion barrier materials are refractorymaterials such as tantalum, tungsten, tantalum nitride, tungstennitride, silicon nitride, titanium, titanium nitride, hafnium, hafniumnitride and the like. As will be more fully discussed hereinbelow thediffusion barrier may be a silicon containing refractory material whichis used in another aspect of the invention to provide a robust barrierlayer.

[0050] Referring to FIG. 1B, diffusion barrier 11 is surface treatedwith a metal replacing reactant, preferably a silicon reactant, to forma silicon rich surface 12. Silicon may be also formed as a layer on thediffusion barrier 11. The surface treatment may be made by reacting thediffusion barrier 11 with a reactant such as SiH₄ or other gasescontaining a silicon element or an amorphous silicon deposit may beformed on the surface of diffusion barrier 11 by known methods such asplasma enhanced chemical vapor deposition and/or low pressure chemicalvapor deposition.

[0051] Referring to FIG. 1C, the structure of FIG. 1B is reacted with ametal containing reactant such as WF₆ to replace the silicon layer 12with the metal to form a metal (tungsten) rich surface 13 on the surfaceof diffusion barrier 11. Such a reaction may be shown as:

2WF₆+3S_(i)→2W+3S_(I)F₄

[0052] As can be seen in FIG. 1C, the finished coated dielectric 10contains a layer of diffusion barrier layer 11 having a metal (such astungsten) rich surface. Such a structure will be used as shownhereinbelow to deposit a copper or other metal coating on the tungstenrich surface to provide the stud and/or line forming the interconnect.

[0053] Another aspect in the invention is shown in FIGS. 2A-2B wherein,as in FIGS. 1A-1C, a sequence of steps is shown to form a metal richsurface on a dielectric having a diffusion barrier. Accordingly, in FIG.2A, a dielectric 14 has a diffusion barrier 15 which is a refractorymaterial containing silicon or other replaceable metal. A material suchas titanium silicon nitride (T_(I),S_(I) ,N), tantalum silicon nitride(T_(a)S_(i)N), tungsten silicon nitride (WS_(i)N), and the like isdeposited on the surface of the dielectric 14. The silicon atoms in thediffusion barrier layer 15 are shown as numeral 16.

[0054] The structure of FIG. 2A is reacted as above for FIGS. 1A-1Cusing a metal containing reactant such as WF₆ to replace silicon atoms16 in the diffusion barrier 15 with the metal to form a metal richsurface 17, which for WF₆ is tungsten.

[0055] The final structure is shown in FIG. 2B and comprises adielectric layer 14, a silicon containing diffusion barrier layer 15 onthe surface thereof with a tungsten rich surface 17 on top of thediffusion barrier layer 15. This structure, as in FIGS. 1A-1C, will beused to deposit copper or other conductor on the surface thereof to forma stud or line interconnect in an electronic component.

[0056] The methods used to form the structures shown in FIGS. 1A-1C and2A-2B offer many advantages. A uniform thin tungsten or other metallayer can be formed on the top of the diffusion barrier, typically lessthan 100Å. This metal layer is in effect is a robust double structurediffusion barrier since tungsten is also another excellent diffusionbarrier for the prevention of copper diffusion. Excellent step coverageof the tungsten layer can also be obtained since this method is asubstitution of silicon and is not a conventional chemical vapordeposition from a gas phase. Additionally, tungsten has a lowerresistivity than most of the barrier metals such as T_(a), T_(a)N, Ti,TiN, WN, SiN, and the like and thus a lower via contact resistance canbe obtained using the barrier layer formed by the method of the subjectinvention.

[0057] Referring now to FIGS. 3A-3G, a sequence of steps is shown toform a line and stud interconnection using a dual Damascene process. InFIG. 3A a lower dielectric layer 18 is shown having a metal conductor 19therein. An upper dielectric layer 20 is on the lower dielectric layer18 and has an opening or via 21 through to the metal conductor 19 and anopening or trench 24. The via has side walls 22 and a base 23 and thetrench 24 has trench side walls 25. This is a typical dual Damascenestructure formed in a multilayer electronic component such as a VLSI andULSI integrated circuit device.

[0058] Referring to FIG. 3B, the structure of 3A is coated with adiffusion barrier layer 26 which covers the upper dielectric layer 20including the via side walls 22 and 23 and trench side walls 25.

[0059] In FIG. 3C a reactant such as SiH₄ is used to form a silicon richsurface 27 on the surface of diffusion barrier 26. In FIG. 3D a reactantsuch as WF₆ is shown to react with the silicon rich surface 27 to form atungsten rich surface 28.

[0060] The tungsten rich surface 28 of the structure is now ready asshown in FIG. 3E for deposition of a copper or other metal seed layer 29which may be applied using known techniques such as PVD, CVD,electroless deposition and electrolytic deposition. The purpose of thecopper seed layer is to promote deposition of copper to fill the via andtrench.

[0061]FIG. 3F shows electroplated copper 30 over the structure coveringthe copper seed layer 29 and filling the trench 24 and via 21. Thecopper seed 29 is shown using a dotted to indicate that theelectroplated copper 30 and copper seed layer 29 form a single metalstructure.

[0062] The structure of FIG. 3F is now typically planarized usingchemicalmechanical polishing and the final interconnect structure madeaccording to the invention is shown in FIG. 3G wherein the lowerdielectric layer 18 having a metal conductor 19 therein is electricallyconnected to via 21 and trench 24 in upper dielectric layer 20. The via21 and trench 24 comprise an outer layer of a diffusion barrier 26, aninner layer of a tungsten rich surface 28 and the electroplated copperlayer 30 filling the via 21 and trench 24. Such a structure provides aninterconnect with excellent step coverage, uniformity, low resistanceand adhesion to CVD-copper and provides an electronic component havingexcellent electromigration resistance and other operating properties.

[0063]FIG. 4 shows a multilayer interconnect structure of an electroniccomponent of the invention comprising a lower dielectric layer 31 havinga conductor 32 therein. Intermediate dielectric layer 33 has a via 36comprising a diffusion barrier 34, a tungsten layer 35 and a copperconductor 37. The intermediate layer 33 is sandwiched between an upperdielectric layer 38 having a conductor 39 therein. As can be seen fromFIG. 4, the via has a double structure diffusion barrier comprising adiffusion barrier material 34 and a tungsten layer 35 and providesexcellent electrical properties and provides the interconnect betweenconductor 32 in dielectric 31 and conductor 39 in dielectric 38.

[0064] While the present invention has been particularly described, inconjunction with a specific preferred embodiment, it is evident thatmany alternatives, modifications and variations will be apparent tothose skilled in the art in light of the foregoing description. It istherefore contemplated that the appended claims will embrace any suchalternatives, modifications and variations as falling within the truescope and spirit of the present invention.

[0065] Thus, having described the invention, what is claimed is:

1. An interconnect structure in a multilayer electronic component forconnecting metallization layers, the interconnect structure havingexcellent step coverage, uniformity, low resistance and adhesion toCVD-copper comprising: a dielectric layer having a through opening to aconductor in another layer; a diffusion barrier layer in the throughopening in the dielectric layer; a metallic layer on the diffusionbarrier layer; and copper filling the opening to form the interconnectstructure.
 2. The interconnect structure of claim 1 wherein thediffusion barrier has metal replaceable atoms on the surface thereofwhich are replaced by the metallic layer.
 3. The interconnect structureof claim 2 wherein the metal replaceable atoms are silicon atoms.
 4. Theinterconnect structure of claim 3 wherein the silicon atoms are formedby surface treating the diffusion barrier layer.
 5. The interconnectstructure of claim 3 wherein a layer of silicon is deposited on thediffusion barrier layer.
 6. The interconnect structure of claim 3wherein the diffusion barrier material contains silicon atoms.
 7. Theinterconnect structure of claim 3 wherein the metallic layer istungsten.
 8. A multilayer electronic component integrated circuit devicecomprising: a plurality of dielectric layers having metallizationtherein; openings in the form of a trench and/or via extending throughat least one layer and connecting metallization in another layer; adiffusion barrier in the opening on the dielectric layer; a metalliclayer on the diffusion barrier layer; and copper filling the opening toelectrically connect the metallization in the dielectric layers.
 9. Thedevice of claim 8 wherein the diffusion barrier has metal replaceableatoms on the surface thereof which are replaced by the metallic layer.10. The device of claim 9 wherein the metal replaceable atoms aresilicon atoms.
 11. The device of claim 10 wherein the silicon atoms areformed by surface treating the diffusion barrier layer.
 12. The deviceof claim 10 wherein a layer of silicon is deposited on the diffusionbarrier layer.
 13. The device of claim 10 wherein the diffusion barriermaterial contains silicon atoms.
 14. The device of claim 10 wherein themetallic layer is tungsten.
 15. A method for making multilayerelectronic component integrated circuit devices wherein interconnects inthe devices have excellent step coverage, uniformity, low resistance andadhesion to CVD-copper comprising the steps of: forming a multilayerelectronic component layer by layer with dielectric layers havingopenings therein with metallization formed in the openings to provideelectrical connections between the layers; forming a diffusion barrierlayer in the opening on the dielectric layer; forming a metallic layeron the diffusion barrier layer by reacting the barrier layer with ametal containing reactant; and filling the opening with copper toprovide a conductor which contacts the metallization in the dielectriclayer to another layer.
 16. The method of claim 15 wherein the diffusionbarrier layer is surface treated to form silicon atoms on the surfacethereof.
 17. The method of claim 16 wherein the diffusion barrier layeris surface treated by contacting the barrier layer with a siliconcontaining reactant to form silicon atoms on the surface thereof. 18.The method of claim 17 wherein the silicon containing reactant is SiH₄.19. The method of claim 15 wherein a layer of silicon is deposited onthe diffusion barrier layer.
 20. The method of claim 15 wherein thediffusion barrier material contains metal replaceable atoms.
 21. Themethod of claim 20 wherein the metal replaceable atoms are silicon.